Most prior art photographic methods requiring high sensitivity rely largely on the use of silver halide photographic emulsions. Such silver halide photographic emulsions are generally characterized not only by their high sensitivity, but by their high quality images and speedy reactions; however, these emulsions require a considerable amount of silver for the image production or, in the case of color photographic systems, for the intermediate medium for the formation of color images.
Photographic methods based upon the use of silver halides usually do not provide a means for recovery or reuse of the silver component, making these methods rather expensive, especially in recent times which have been characterized by dramatic increases in silver prices. Hence, it would be highly desirable if alternative photographic methods were available therein the use of silver is minimal or, better still, eliminated, while maintaining, or even improving upon, the image quality produced by silver based photographic methods. To this end, many substitutes for silver based photographic materials have been tried, for it is well known that many other metallic salts are photosensitive. In particular, copper has been the subject of great deal of research aimed at replacing silver in various photographic systems. However, to date, research in this area has failed to produce copper compounds having photosensitive properties which even marginally approach those of silver. For example, most prior art copper salt systems have generally failed to provide sharp, fog free, continuous tone, stable images.
Of all the copper salts which have been investigated, cuprous halide compounds probably have been the subject of the most intense study. Some representative examples of the results of this research include:
1. U.S. Pat. No 4,350,758, which is typical of a number of references, teaches the use of a mixture of silver halide and copper halide (e.g. CuCl) salts to prepare photosensitive emulsions. The copper halide is formed by conventional chemical precipitation methods which do not include the electrolytic deposition of a sensitive copper materials as described in the present invention. PA1 3. U.S. Pat. No. 4,433,049 teaches utilization of an ascorbic acid halide derivative (similar to that disclosed in U.S. Pat. No. 4,427,762) to reduce cupric ions in a liquid phase to form photosensitive cuprous halides. There is no disclosure of a photosensitive material obtained by electrolysis. PA1 4. U.S. Pat. No. 3,671,249 teaches a process for preparing a photosensitive cuprous nitrate composition by reacting cuprous halide (e.g. CuCl) with silver nitrate to provide a mixture of cuprous nitrate and silver halide. The material of the present invention, on the other hand, is produced by electrolysis, and is not a mixture of materials as described in this reference. PA1 5. Kosar, Light-Sensitive Systems: Chemistry and Application of Non-Silver Halide Photographic Processes, J. Wiley and Sons (NY)--1965, pp. 14-41, teaches the photosensitive nature of CuCl and how this material can be made into photosensitive films through the use of various binders and the like. The use of OuOl obtained by copper electrolysis is not taught or suggested by this reference.
2. U.S. Pat. No. 4,427,762 describes a photosensitive copper (I) halide (optionally mixed with silver halide) in a binder which can be exposed and developed with an alkaline developer (e.g. a mixture of an amine and an ascorbic acid derivative). Formation of a copper (11) complex is disclosed. Here again, the cuprous halide is formed by chemical precipitation reactions which do not include copper electrolysis.
In all of the aforementioned documents, the products obtained do not produce the results obtainable with the present invention; that is, sharp, fog free, continuous tone, stable images in silver-free systems.